In a laser beam printer (LBP), an electrostatic latent image is formed on the photosensitive surface of a rotating drum by scanning the surface with a laser beam modulated in accordance with image information such as text, etc. A hard copy of the image information is obtained from the photosensitive surface by a copy-processing technique that includes development of a sensible image, and its transcription and fixation on a paper sheet. A typical laser beam printer is illustrated in the July 1984 issue of Computers and Electronics in an article entitled "HP's New Laserjet Printer" by Josef Bernard. This article is hereby incorporated by reference.
In the event of a malfunction in a laser printer, such as, for example, a paper jam, this condition is sensed and the mechanical drive is interrupted to allow the malfunction to be corrected. The resultant interruption often occurs during the scanning process while the laser beam is actually writing on the photosensitive surface. Once an interruption occurs, drum rotation terminates with the result that the laser beam impinges upon a fixed region on the photosensitive surface. To prevent local deterioration of the surface, the laser beam must be extinguished upon detection of a malfunction.
Conventionally, the laser is extinguished by shutting down its power supply in response to detection of a malfunction. The problem with this approach is the time required to re-initialize the laser in order to raise its light output to a preselected value after the cause of the malfunction is corrected and the system is re-started.
It is therefore an object of the present invention to provide an emergency resetting circuit for a semiconductor laser driving apparatus which does not suffer from the deficiencies described above.